Incandescent electric lamps and fluorescent lamps are widely used as light sources for illumination devices. In addition to these lamps, illumination devices using a semiconductor light-emitting element such as a LED or an organic EL (OLED) as a light source have been developed and used in recent years. Since a variety of emission colors can be obtained with those semiconductor light-emitting elements, the development and use of illumination devices in which a plurality of semiconductor light-emitting elements with different emission colors are combined and the emission colors thereof are combined to obtain the radiated light of the desired color have been started.
Patent Document 1 describes an example of a semiconductor light-emitting device that uses a violet light-emitting diode element and emits light with a correlated color temperature equal to or higher than about 2700 K and equal to or lower than 4000 K and a general color rendering index Ra (referred to hereinbelow simply as Ra) equal to or greater than 80.
Patent Document 2 describes a pseudo-flame type light-emitting device that has a core section with an external shape resembling a candle flame, an inner flame section, and an outer section. The color temperature of the outer flame section of the device described in Patent Document 2 is 1000 K to 2200 K. It is also indicated that in order to obtain the color temperature of the outer flame section within a range from 1000 K to 2200 K, the device described in Patent Document 2 is provided with a light-emitting element emitting blue light in the core section and also provided with a phosphor (more specifically, an YAG (Yttrium Aluminum Garnet) phosphor) emitting yellow to yellow-red light in the outer flame section.
Patent Document 3 describes an illumination device with an outer shape resembling a candle and candle flame that emits light with a correlated color temperature of about 1500 K. The illumination device described in Patent Document 3 includes a light source module constituted by two light-emitting elements. Each of the two light-emitting elements has a plurality of light-emitting unit layers emitting monochromatic light rays of different wavelengths, and the emission intensity at each wavelength corresponding to the number and thickness of the light-emitting unit layers is adjusted to bring the distribution of the light emission spectrum to that of the solar light spectrum and increase the Ra.
Patent Document 4 describes a light-emitting device provided with a blue LED with a peak wavelength of 470 nm to 480 nm and a fluorescent substance with a peak wavelength of 600±3 nm and emitting light with a color temperature of 1900 K to 2100 K.
Patent Document 5 describes a light source provided with a blue GaN (Gallium Nitride) LED, a red quantum dot substance, and a yellow-green phosphor substance and emitting light with a color temperature of 1000 K to 16000 K. Patent Document 5 indicates that a color rendering index (CRI) can be set to a desired value by selecting the type and configuration of the LED, quantum dot substance, and phosphor substance.
Patent Document 6 describes a LED illumination lighting fixture in which three blue LED with a peak wavelength of about 480 nm are used as a light emission source, and phosphors coated on each of the blue LED emit respective fluorescence. In the LED illumination lighting fixture described in Patent Document 6, a mixture of a green phosphor and a red phosphor is coated on two blue LED from among the three blue LED, and a yellow phosphor is coated on the remaining one blue LED. The LED illumination lighting fixture described in Patent Document 6 radiates a combination light of the blue light emitted by each blue LED and fluorescence emitted by each phosphor.
Patent Document 7 describes an illumination device provided with a violet LED, and a light-emitting body obtained by mixing a blue phosphor, a green phosphor, and a red phosphor, each emitting fluorescence obtained by wavelength conversion of part of the light emitted by the violet LED. The illumination device described in Patent Document 7 radiates combination light of the light emitted by the violet LED and the fluorescence emitted by the light-emitting body.    Patent Document 1: WO 2011/024818    Patent Document 2: Japanese Patent Application Publication No. 2005-78905    Patent Document 3: Japanese Patent Application Publication No. 2004-128443    Patent Document 4: Japanese Patent Application Publication No. 2009-64999    Patent Document 5: Japanese Translation of PCT Application No. 2008-544553    Patent Document 6: Japanese Patent Application Publication No. 2009-123429    Patent Document 7: WO 2008/001799
When a semiconductor light-emitting device using a semiconductor light-emitting element such as a LED as a light source is used as an illumination device for indoor illumination such as indirect illumination, candle color light should be emitted at a high value of Ra (more specifically, light with a correlated color temperature equal to or higher than 1600 K and lower than 2400 K, preferably lower than 2000 K).
However, Patent Document 1 does not describe a device that emits light with a correlated color temperature equal to or higher than 1600 K and lower than 2400 K.
Further, Patent Document 2 and Patent Document 4 do not describe a configuration for increasing the Ra, or a research aimed at the development of such a configuration.
In the illumination device described in Patent Document 3, light emitted only by a special light-emitting element is radiated. The resultant problem is that a circuit for controlling the output of the light-emitting element is necessary and the cost of production and the like increases. Another problem is that color separation easily occurs due to a strong directionality of the light emitted by the aforementioned light-emitting element.
Patent Document 5 does not describe a configuration for increasing the Ra in a device emitting light with a correlated color temperature equal to or higher than 1600 K and lower than 2400 K, or a research aimed at the development of such a configuration.
The LED illumination lighting fixture described in Patent Document 6 uses blue LED that emits light with a wavelength longer than that of a violet LED as a light emission source. The resultant problem is that the emission efficiency is low. Further, since a mixture of phosphors is coated on a single blue LED so as to emit light including a large number of red components, the candle color light with a sufficiently high Ra cannot be emitted.
In the light-emitting device described in Patent Document 7, color rendering capacity in a red region is increased, but a method for further increasing the color rendering capacity of the candle color light, which is the light with a lower correlated color temperature, is not described.
With the techniques described in Patent Documents 1 to 7, the visual feeling created by the light sources is inadequate when compared with the natural candle, and the emitted light seems unnatural for the candle color, for example, because of bluish coloration.